Electric resistance element and method of making the same



APPLICATION FILED MAR- II 19!? Patented Mar. 29, 1921.

INVENTOR Ral h E. Ma /"b 0/30.

WITNESSES: Q. &

ATTRNEY UNITED STATES RALPH E. MARBURY, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSE ELECTRIC AND MANUFACTURING COMPANY, A

SYLVAN IA.

CORPORATION OF PENN- ELECTRIC RESISTANCE ELEMENT AN D METHOD OF MAKING THE SAME.

To all whom it may concern:

Be it known that I, RALPH E. MAnnURY, a citizen of the United States, and a resident of VVilkinsburg, in the county of Allegheny and State of Pennsylvania, have 1nvented a new and useful Improvement in Electric Resistance Elements and Methods of Making the Same, of which the following is a specification.

My invention relates to reslstance elements and more particularly to elements offering extremely high resistance to the flow of electric currents.

In connection with radio sets, it is neces sary to employ very high resistance as grid leaks. A further adaptation of an extremely high resistance is found in a leakage to be employed across a condenser. It has been found difiicult to provide resistances adapted for use as above mentioned which are stable under atmospheric changes to the extent of approximately 15 C. to 30 or 40 0. temperature rise. In view of this, one object of my invention is to provide a resistance which will maintain sub-- stantially a constant value under such temperature changes.

Another object of my invention is to provide an electrical-resistance element in which the resistivity may be accurately adjusted in a simple manner.

With these and other objects in view, my invention will be more fully described, illustrated in the drawings, in the several views of which corresponding numerals indicate like parts, and then particularly pointed out in the claims.

In the drawings, Figure 1 is a longitudinal, sectional view of a resistance tube embodying a resistance element provided by my invention; Fig. 2 is a cross sectional view taken substantially along the line IIII of Fig. 1, and Fig. 3 is a cross sectional view taken substantially along the line IIIIII of Fig. 1.

The broad object of my invention is to provide a resistance element in which the resistance may be adjusted to values rang ing from 2 megohms to 7 megohms. Although these are the values usually desired in such resistance elements, the resistance provided by my invention may be regulated to have values considerably lower than this. In order to set forth a practical manner in Specification of Letters Patent.

Application filed March 11, 1919.

Patented Mar. 29, 1921. Serial No. 281,915.

which my resistance element may be embodied in a structure, I have shown, in the drawings, a tube containing a resistance element embodying my invention. The particular structure of the inclosing tube, however, forms no part of my invention and Wlll only be described briefly in order to set forth a. desirable manner of employing the resistance element.

I may provide a resistance element by employing a fibrous material which may preferably be in the form of a. relatively stiff cardboard which may be subjected to a bath comprising a colloidal solution having a comminuted conducting material suspended therein. I prefer to employ a good grade of drawing ink, such as Staffords or other well known india inks, to which may be addedconducting material, such as graphite or titanium carbid. A fibrous material impregnated with ink containing either graphite or titanium carbid offers a highrcsistance to the flow of electric current, and the resistance thereof may be varied to some extent by merely erasing a portion of the ink after the card has been impregnated therewith. The ink possesses a sufiicient degree of conductance to limit the resistance of a small element to approximately 3 megohms. However, this resistance may be increased to any desired value by adding shellac to the ink. I have found that, by adding small quantities of shellac to the ink, a resistance element having a value of substantially 7 migohms may be provided.

resistance element may be constructed which possesses exceptionally stable characteristics, under temperature changes between 10 and 40 0., by employing a solution of ink and finely divided titanium carbid. I have found that satisfactory proportions in which the solution may be provided may be obtained by employing approximately 20 cubic centimeters of ink and 1.5 grams of titanium carbid. These proportions, however, depend upon the degree of resistivity desired in the resistance element. It will be apparent that the greater the quantity of titanium carbid, the less the resistivity of the resistance element will be.

A satisfactory resistance element may also be constructed by employing 'a solution of ink and graphite. Although the graphite imparts less stable characteristics to the resistancc element under temperature changes,

it also facilitates the production of uniform resistance elements from a solution utilized at intervals.

In some instances, it is desirable to obtain a very high resistance amounting to almost open circuit. Such resistances are difiic-ult to obtain but I have found that a very high resistance may be provided by employing a good grade of lndla ink to which may be added a small amount of shellac. The shellac is preferably mixed with the ink, after which a suitable card of fibrous material may be impregnated with the mixture. Obviously, the resistance of the element may be increased by increasing the proportion of shellac added to the ink. Such a solution is suitable for very high resistances, such as those having a value approximating 7 megohms,

After a resistance element has been provided, as above described it is preferably disposed within av protective casing sulficiently tight in the joints thereof to exclude moisture. I have shown such a casing in the drawings in which 1 is a fiber rod tapped to receive studs 2 of suitable conducting material. The rod and studs are preferably machined to provide a substantially fiat intermediate portion upon which a resistance element 3, embodying my invention, may be secured. The resistance element 3 is secured to the fiber rod 1 by screws L extended through the machined ends of the studs 2 and the portion of the fiber rod beneath these ends. A glass tube 5 may be disposed to inclose the fiber rod 1 and may be held in place by brass caps 6 screwed upon the studs 2. It has been found advantageous to employ paraflin or other suitable wax to seal the ends of the glass tube engaged by the brass cap-s.

A resistance element constructed in accordance with my invention and disposed in an inclosing casing, such as above described, maintains a constant value of resistance under any temperature rise experienced with normal operating conditions. In case it is desirable, the resistance element may be removed from the casing and readily replaced or its value of resistance may be easily changed by removing the protective glass tube and erasing a small quantity of the ink.

Although I have described a resistance element which may be provided by my invention, it is obvious that various proportions may be employed in solutions with which fibrous materials may be impregnated to construct a resistance element in accordance with my invention and I desire, therefore, that no limitations shall be imposed except such as are indicated in the appended claims.

I claim as my invention:

1. An electrical resistance element comprising fibrous material impregnated with a colloidal solution and acomminuted'conducting material suspended therein.

2. An electrical resistance element comprising fibrous material impregnated with a colloidal solution and titanium carbid suspended therein.

2 3. An electrical resistance element comprising fibrous material impregnated witli a 'c-olloidal solution and comminuted titamum carbid suspended therein.

f. An electrical resistance element comprising a fibrous material impregnated with ml: containing titanium carbid.

5. An electrical resistance element-comprising fibrous material impregnated with ink containing finely divided titanium carbid.

6. An electrical resistance element comprising fibrous material impregnated with a solution including india ink and commlnuted titanium carbid in substantially the proportions of twenty cubic centimeters of india ink to one and five-tenth grams of titanium carbid.

7. An electrical resistance element comprising fibrous material impregnatedv with ink containing a substance capable of varying the resistivity of the ink.

In testimony whereof, I have hereunto subscribed my name this 28th dayof Feb. 1919. t

RALPH E. MARBURY. 

